Magnesium variability extends findings to Earth’s past temperatures

SAN FRANCISCO–A new study affirms that magnesium variability is linked to the day/night, namely light/dark, cycle in simple, single-celled forams and extends the findings to more complex multi-chambered foraminifera.

The new findings, published in the journal Nature Communications, are related to one of the most common methods for obtaining data about the Earth’s past temperature, as it is derived from the remains of tiny marine organisms called foraminifera found in oceanic sediment cores.

These forams are sand-grained-sized marine protists that make shells composed of calcite. When they grow, they incorporate magnesium from seawater into their shells. When ocean temperatures are warmer, forams incorporate more magnesium, and less when the temperatures are cooler. So, scientists can tell from the amount of magnesium what the temperature of the seawater was thousands, even millions of years ago.

However, studies of live forams reveal that shell magnesium can vary, even when seawater temperature is constant.

In their study, researchers from Oregon State University (OSU), University of California, Davis, University of Washington and Pacific Northwest National Laboratory, grew the multi-chambered species, Neogloboquadrina dutertrei, in a laboratory under highly controlled conditions. They used high-resolution imaging techniques to “map” the composition of these lab-grown specimens.

“We found that high-magnesium is precipitated at night, and low-magnesium is added to the shells during the day,” said Jennifer Fehrenbacher, an ocean biogeochemist and paleoceanographer at OSU.

“This confirms that magnesium variability is driven by the same mechanism in two species with two different ecological niches. We can now say with some level of confidence that magnesium-banding is intrinsically linked to shell formation processes as opposed to other environmental factors.”

As lead author on the study, Fehrenbacher was quoted as saying in a news release that “the variability in magnesium content of the shells doesn’t change the utility of forams as a proxy for temperature. Rather, our results give us new insights into how these organisms build their shells and lends confidence to their utility as tools for reconstructing temperatures.”